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jeffyjeep
10-21-2009, 09:49 AM
Does anyone make a 3 G cluster kit to go into a BT-80? Also, I assume that a G engine is 29mm--am I correct? Jeff

Doug Sams
10-21-2009, 10:41 AM
Does anyone make a 3 G cluster kit to go into a BT-80? Also, I assume that a G engine is 29mm--am I correct? JeffYes, for all intents and purposes (or intensive purposes http://forums.rocketshoppe.com/images/smilies/biggrin.gif ) G motors are 29mm (or larger). I believe there have been a couple of odd ball 24mm units - maybe even an 18 - but they're all long gone.

If you get three of the thin-walled 29mm motor tubes (ala LOC), they will fit, albeit snugly, into a BT-80. But the thicker-walled units (ala PML) are a no-go.

Take a look at page 6 in this doc to get an idea of what it looks like: http://www.doug79.com/stuff/BT-80Clusters.pdf

BTW, the LOC-type 29mm MMT has a wall thickness of 0.035" (& OD of 1.21"). Several vendors carry this size including BMS (T52H-34). The thicker PML (phenolic) style has a wall thickness of 0.062" (& OD of 1.269").

HTH.

Doug

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jeffyjeep
10-21-2009, 10:54 AM
Thanks Doug. Jeff

Doug Sams
10-21-2009, 11:00 AM
Thanks Doug. JeffBTW, Jeff, sorry I didn't get it all answered. I can't tell you if anyone makes a motor mount kit in 3x29, but, since the tubes will fit tightly into the airframe, no centering is required. All you need to do is plug the voids, and you can do that several ways. The old tissue and glue technique works. I've also rough-cut plugs from thin, soft plywood (eg, lite-ply) and sanded them to shape using a piece of 100-grit wrapped around a motor tube.

HTH.

Doug

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GregGleason
10-21-2009, 11:05 AM
Jeff,

I don't know of any kits. But scratchbuilding one should be easy enough to do.

You can't do it with a BT-80 for RMS motors, because you are constrained by the aft closure diameter. The minimum ID tube that could fit in is 2.6503 inch (according to my CAD program and AeroTech dimensional drawings).

However, you can do it with SU motors. If you place the motors next to each other without motor tubes, a set of 3 x SU motors could fit in an ID as small as 2.4240 inch. With thin wall motor tubes you might be able to friction fit them inside the BT-80 airframe.

Greg

GregGleason
10-21-2009, 11:21 AM
BTW, given that that an Estes BT-80 has an ID of 2.588 inches, the largest diameter that a cluster of 3 x tubes can accommodate is a diameter of 1.2011 inches for each tube.

Greg

sandman
10-21-2009, 12:15 PM
Keep in mind that 3 "G's" would be considered High Power.

You would have to be Level 1 to launch that at a sanctioned event.

But you probably know that.

As for fit, you would probably have a lot less trouble with a LOC or PML 3" tube.

My 2 cents.

Doug Sams
10-21-2009, 02:25 PM
BTW, given that that an Estes BT-80 has an ID of 2.588 inches, the largest diameter that a cluster of 3 x tubes can accommodate is a diameter of 1.2011 inches for each tube.Greg,

It's even tighter than that, but it can still be made to fit with only a little distortion.

The number cited, 2.588, looks like it came from Rocksim (which is wrong). The actual ID of BT-80 is 2.558 (subtracted from 2.600 gives 0.042 for an 0.021" wall, FWIW). So it's even tighter. But three LOC 29's can be made to fit with minimal distortion.

It's not ideal, but when the rubber meets the road, it's good enough http://forums.rocketshoppe.com/images/smilies/smile.gif That is, it can be done without any special parts - no special ordering, no custom cutting, no shipping charges http://forums.rocketshoppe.com/images/smilies/smile.gif - just the tubes and a very old fashioned plugging technique from the Astron Ranger.

(That said, and as noted by Sandman, given that it's HPR, it'd probably be better to use LOC 2.56" tube instead of BT-80. That's a much better match for that level of impulse.)

Doug

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GregGleason
10-21-2009, 02:47 PM
... The number cited, 2.588, looks like it came from Rocksim (which is wrong).



Well, you are not going to believe where I got that number:

The 2008 Estes Catalog (.pdf version).

I had to go back to the file to see if I did a number transpo, but I didn't.

Since we are talkin' paper tubes we can get away with it, but it would be a no-go if we were in the realm of aluminum. It just doesn't flex as much. :D

Instead of using the LOC tube, you could toss on a wrap or two of fiberglass (or even CF!). But I agree, if you were running 3 x G80s on standard Estes tube you might be asking for a shred. Because that baby is going to haul BIG TIME if all of those motors come up to pressure at the same time. :eek:


Greg

Doug Sams
10-21-2009, 03:13 PM
Instead of using the LOC tube, you could toss on a wrap or two of fiberglass (or even CF!). Everybody tries that...once http://forums.rocketshoppe.com/images/smilies/smile.gif After you've done it, and added it your skill set and rocketeer resume, you then realize that evening (and 7 bucks worth of supplies) spent glassing a BT-80 woulda bought you the LOC 2.56 and left you with an extra hour to do something else http://forums.rocketshoppe.com/images/smilies/smile.gif

Seriously, I think most of us have done it a few times. But after a while, you start looking for short cuts http://forums.rocketshoppe.com/images/smilies/smile.gif

Doug

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Green Dragon
10-22-2009, 11:20 AM
3 x 29mm into BT80 or similar is not an issue.

might distort the tube slightly, but then you fill the voids with paper soaked in CA and an epoxy cap, and ... no problems.

What you describe is basically the old Enerjet 2650 ( and thereby applicable to Old rockets ;) ) .

there should be an assortment of Kits available for this.

2650 type birds or possibly clustered inside ( ala US Rockets WARP3 ) .

as for rings- you could use a wood ring with holes spaced to act as gas seals - say an 'even spaced" 3 x 24mm Sunward ring.

3 Gs is pretty ambitious though :D .... been there, lost a 2650 on 3 x G78s at LDRS 6, have flown that on Gs a few times prior.. always a mile + boost :D

now I just fly 3Gs in my LOC Minnie Viper, lot less chance of loss :)

~ AL

snaquin
10-22-2009, 08:16 PM
3 Gs is pretty ambitious though :D .... been there, lost a 2650 on 3 x G78s at LDRS 6, have flown that on Gs a few times prior.. always a mile + boost :D

~ AL

I think I went way past ambitious when I loaded three H35-10J single use motors in my 2650 clone at LDRS but hey, smoke em' if you got em' .....

Mine was build using all LOC parts and was true to scale to the drawings Gary Rosenfield made at Composite Dynamics. Only the LOC nose cone wasn't scale so I had to adjust the overall length just a little.

I would agree with the earlier suggestions that LOC MMT-1.14 motor tubes in the LOC BT-2.56 airframe are a very nice fit and I have built two 2650 clones using these components. I didn't use a plate with holes in front the motor tube on either of my 2650 builds trying to recreate my model per the plans. I stuffed some paper towel pieces between the gaps and recessed that about 1/8" from the airframe aft end and topped all three spaces with a little epoxy to seal it. It doesn't take much and leveled out well.

http://forums.rocketshoppe.com/showpost.php?p=3284&postcount=1

I have parts to build another and would choose LOC components again for fitting three 29mm mounts in a BT-2.56 airframe because I found it worked very well for me.

:)

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Green Dragon
10-22-2009, 09:04 PM
awesome pic Steve :D

amazing how those vintage cluster pics look al Kick A**, even with M's and other large motors about now.

I always drool over old pics in HPR, etc of the old cluster birds ... guess it's an illness.

My 2650 I lost at Hartsel was a US Rockets version,no payload ( so short and light to boost :D ).

Need to build another, to go with my 2250 clone Lee signed at NARAM 50 .

especially if the Quest motors arrive - 3 X F12 black powder :)

~ AL

hmm. lot of smiles in that post, what's up with that ? :D